Abstracts of STEP-4
keynote
Schrödinger's cat and a role of adsorbed water from humidity on contact charging
Daniel J. Lacks
Case Western Reserve University, USA
We use first principles quantum mechanical calculations to address the charge distributions in water sandwiched between oxide surfaces. We find that the water molecules accumulate positive charge. Upon separation of the surfaces, the water molecules can desorb with a certain probability of taking away charge.
Attenuation of signals due to charged particles in sand/dust storms1
Jùn Zhou, Xuqiang Dou, Li Xie2
College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000, China
Key Laboratory of Mechanics on Environment and Disaster in Western China, Ministry of Education, China
1 This research work is funded by Innovative Research Group of the National Natural Science Foundation of China (No. 11421062) and by grants of the National Natural Science Foundations of China (Nos.11472122, 11272139). The authors would like to express their sincere appreciation of these supports
2 Corresponding author, email: xieli@lzu.edu.cn
In sand/dust storms, it has been found that sand/dust particles are usually charged due to several reasons, e.g., the collisions between sand/dust particles. In this study, scattering of electromagnetic waves by charged particles is investigated, where the scattering problem of electromagnetic waves by partly and overall charged spherical particles is solved based on Mie scattering theory. The effect of charged sand/dust particles on the scattering properties of signals, including the attenuation of signal and Radar Back Scattering Cross Sections, is studied, for both overall charged particles and partly charged particles in sand/dust storms. It is found that the scattering properties, such as the attenuation of the signal and the back scattering cross section, are significantly affected by the charges carried on by the sand/dust particles, as compared with uncharged particles. And, for the cases that the wavelength is much larger than the size of the particles, the effect of charged particles on the attenuation and the back scattering is maximal when the overall surfaces of the particles are charged. Compared with the existing results of charged particles which was based on Rayleigh scattering theory, our results obtained in this study is reasonable from the viewpoint of physics, because the results based on Rayleigh’s theory gave a conclusion that when the particles are overall charged uniformly on surfaces, the scattering of electromagnetic waves by overall charged particles was always not affected by the charges on the surfaces, no matter what the charge density was, which was not tenable from the viewpoint of physics.
Triboelectric charging of particles in a simulated sand storm: Particle density measurements
Henry J. Squire
Case Western Reserve University, USA
Triboelectric charging of windblown sand can generate large electric fields, which in turn can influence the movement of sand in a sand storm. To investigate sand particle density in sand storms, sand was blown from a bed through horizontal, parallel electrodes set at a variety of potentials with a laser positioned at different positions along the electrodes. Visibility, particle number concentration in air, and particle density in air were calculated from the transmitted power of the laser. Calculated particle density varied with applied electric field strength, suggesting net deflection of sand particles.
Effect of charges carried by sand/dust particles on Radar monitoring1
Xuebang Gao, Li Xie2
College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000, China
Key Laboratory of Mechanics on Environment and Disaster in Western China, Ministry of Education, China
1 Supported by the grant of the National Natural Science Foundations of China (No.11472122)
2 Corresponding author, email: xieli@lzu.edu.cn
Radar is a very effective detecting method to monitor sandstorm. In sandstorm detection by a radar system, the receiving power is mainly determined by the absorption and scattering of sand/dust particles. Since sand/dust particles are usually charged, any change in scattering or absorption efficiencies of small charged sand dust particles has the potential to affect the threshold-level data received by radars in the microwave and millimeter-wave spectral range. In this paper, the effect of sand/dust particles charged on the backscattering and attenuation of radar detection wave is discussed at length. Mie scattering is assumed to compute the backscattering radar cross section, which can provide more accurate results for practical regional monitoring of sandstorms. Based on Mie scattering theory and radar meteorological equation, we calculated accurately the effect of sand dust particle charged on radar receiving power and attenuation in different detection bands. It was found that charges carried by particles can increase the receiving power, and the increment is related to the charges, particle size parameter, radar emission frequency, and corresponding refractive index of the particles. As the emission frequency of the radar increases, the effect of the charges on the receiving power decreases, and especially, the effect of charges on the receiving power can be ignored for lidar used to detect sand particles. Moreover, we also discuss the effect of dust particle charged on radar detection distance in detail.
keynote
Characterization of granular electrostatics generation
Yanlin Zhao1, Jun Yao1, Chi-Hwa Wang2
1 Sino-British Joint Energy Research Centre, College of Mechanical and Transportation Engineering, China University of Petroleum-Beijing, Beijing 102249, People’s Republic of China
2 Department of Chemical and Biomolecular Engineering, National University of Singapore, 4 Engineering Drive 4, 117585, Singapore
Granule electrostatics is widely found in most granule engineering areas. However, the working mechanism has never been fully understood due to its sensitivity to working conditions, such as granule geometrical shape (including length-ratio and front-facing angle), contact area, granule material, relative humidity, sliding velocity, sliding orientation and normal stress. In this work, single granule was designed to slide along a metal plate and the electrostatics charges generated were measured via an electrometer connected with a computer. The working factors above have been considered for two kinds of granules made of PVC or coal. Regarding the geometrical factors, it is found that granules with larger length-ratio tend to produce more electrostatics, the slender or sharper granules tend to have higher capability of electrostatics generation and triangular granules generate more electrostatics than trapezoidal granules. In addition, electrostatics increase with decreasing granule front-facing angle and charges tend to gather at the granule tip. Regarding the granule material, it is found that coal granule tends to generate more electrostatics in comparison with PVC granule. The sequence of the relative work function for the three materials used in this work from high to low is given by the following sequence: PVC, stainless steel and coal. Regarding surrounding factors, it is found that electrostatics increases with granule contact area and such trend increases with decreasing relative humidity. Electrostatics generated increases with decreasing relative humidity and sliding velocity. Granule sliding orientation does affect electrostatics. In this work, granules sliding with smaller front-facing angle as well as shorter side tend to generate more electrostatics. Electrostatics increases with normal stress.
Reaction conversion in a microplasma reactor
Joseph R. Toth III
Case Western Reserve University, USA
Plasmas are able to dissociate numerous stable molecules at room temperature without the use of catalysts offering great potential for use as chemical reactors. In order to determine which reactor parameters are important for conversion processes, we studied the conversion of methane at various conditions (power, volume, flow rate) with experiments and simulations. Our results found that volume is not an important parameter in determining the conversion, whereas power and flow rate are both important. This result is consistent with the idea that plasma depend on energy density, which is equivalently the ratio of power to flow rate.
Effects of charged particles on laser signals: An experimental exploration1
Haichao Zhong, Jun Zhou2, Li Xie
College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000, China
Key Laboratory of Mechanics on Environment and Disaster in Western China, Ministry of Education, China
1 Supported by the grant of the National Natural Science Foundations of China (No.11472122)
2 Corresponding author, email: zhoujun@lzu.edu.cn
The sand particles are prone to be electrified and carry some net charges on their surfaces, which leads to a change of the dielectric constant of the sand particles. As we know that the attenuation of the electromagnetic waves by the sand particles system is significantly dependent on the dielectric constant of sand particle. In this paper, we investigated the received power of a laser transmits through a suspend sand/dust system, and then based on the Beer-Lambert law and Koschmieder law, the change of the laser attenuation coefficient in the charge-mass ratio under the same visibility was derived. The experimental results showed that the effect of charged particles on the laser beams with different wavelengths is not exactly same; the larger the charge-mass ratio, the larger the relative change of the extinction coefficient the same wavelengths by charged particles.
Potential applications of triboelectrics to secondary education
Blaire M. Volbers
Case Western Reserve University, USA
It has recently become common for high school students to be encouraged to perform more "inquiry-based" labs and classroom activities in order to better develop their critical thinking skills. For the past five weeks, we have been studying saltation and charging of windblown sand using a lab scale model at Lanzhou University. What potential applications could scientific research such as this have for high school students and how could it be better incorporated into the classroom?
keynote
Charging of multiple particles in a shaker
Tatsushi Matsuyama
Soka University, Japan
The experiments are simple. Multiple particles are shaken in a metal capsule. After a certain time of the shake, generated total amount of charge, supposed to be a saturation charge, was measured with Faraday-cage. Although the total amount charge increases with an increase of the number of particles set in a shaker, the charge per particle reduces. This is supposed due to space charge effect: when a particle is in contact with a metal wall, external electric field from the other charged particles affects the charge transfer on the contacting particle. Note that the net charge injection comes from capsule wall, even if particle to particle contacts changes charge distribution among particles. By this effect, the saturated charge per particle becomes a function of the number of particles and capsule size.
Experiments were conducted with teflon spherical particles of 2-4 mm in diameter, with single size for each experiment, and glass beads, alumina and zirconia beads of 100-300 µm. For the teflon particles, or relatively bigger particles, a master curve was obtained to estimate the charge per particle as a function of particle volume ratio in the capsule and capsule size. However for inorganic particles, or smaller particles, the unify of empirical formula to explain the experimental results was not perfect, although the tendency was similar. This will be discussed in details. Additionally an ongoing project of DEM modeling for these system will also be discussed.
Numerical investigation of effects of electromagnetic wave attenuation by charged sand particles1
Xvqiang Dou, Li Xie2, Jùn Zhou
College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000, China
Key Laboratory of Mechanics on Environment and Disaster in Western China, Ministry of Education, China
1 Supported by the grant of the National Natural Science Foundations of China (No.11472122)
2 Corresponding author, email: xieli@lzu.edu.cn
When the electromagnetic waves (EMWs) propagate through the particles and particle system, such as the dust&sand, haze, mist aerosol etc., two attenuate mechanisms of EMWs will occur, such as scattering and absorption (extinction=scattering+absorption), which results in the intensity of the signal attenuated and the distance of the transmission shorten. Many factors could affect the extinction efficiency, such as the charge carried on the particle, the ambient relative humidity, the shape and the radius of the particles, the frequency of the incident EMWs and the temperature, in this paper we calculated the attenuation of the EMWs considering the all factors mentioned above. It revealed that the attenuation of the EMWs becomes larger when the EMWs propagate though the charged-particle dust&sand system than EMWs propagate though the without-charged-particle dust&sand system. The attenuation becomes larger in the humid environment than in the dry air, which also depends on the particles size.
Modeling of adhesion forces of particles on rough surfaces
Qizan Chen
Case Western Reserve University, USA
The adhesion of particles to surfaces depends on a number of factors, including electrostatic forces. Here we examine the electrostatic contributions to adhesion for charged dielectric particles to a metal surface. While this problem has been addressed for spherical particles on smooth surfaces, we use finite element modeling to determine the electrostatic contributions to adhesion for particles that are non-spherical and for surfaces that are non-smooth, as a function of the dielectric constant of the material, the particle shape, and the surface roughness.
Monte Carlo simulation of multiple scattering effects of electromagnetic waves by charged dust particle system1
Zhixin Du, Li Xie2
College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000, China
Key Laboratory of Mechanics on Environment and Disaster in Western China, Ministry of Education, China
1 Supported by the grant of the National Natural Science Foundations of China (No.11472122)
2 Corresponding author, email: xieli@lzu.edu.cn
In recent years, Monte Carlo method has quickly become the best method for simulating electromagnetic waves propagation in a medium. In this paper, based on Monte Carlo method, the transmittance of electromagnetic waves propagating through sand and dust systems is simulated considering the multiple scattering effect under different visibility. We found that when the charges carried by the sand particles considered, it makes the multiple effect of the electromagnetic waves stronger, and it should consider the multiple scattering when sand particles carry net charges on their surfaces, even if it is not necessary to consider the multiple scattering effect when the sand particles are neutral. That means the charges carried on the sand particles make the critical visibility to consider the multiple scattering effect increased. The critical visibility to consider the multiple scattering effect related to the charges is discuss for the sand/dust particle system.
An experimental investigation of sand particle flux in a vertical pipe under different electric field1
Cheng Zhou, Li Xie2
College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000, China
Key Laboratory of Mechanics on Environment and Disaster in Western China, Ministry of Education, China
1 Supported by the grant of the National Natural Science Foundations of China (No.11472122)
2 Corresponding author, email: xieli@lzu.edu.cn
Granular matter, which can both have similar to solid and liquid behavior, is a very interesting dynamical system. Their specific properties between particles can be attributed to the friction and inelastic collisions. Granular flow is nonlinear system, it hasn’t been explained with a good theory. This system is widely applied to nature and technology application, such as mining, agriculture and construction, as an example in complex systems. In this paper, we experimentally investigate the effects of sand flow in a vertical pipe with a horizontal electric field. The experimental results show that the change of electric field intensity has no effect on the flow of sand. However, the charge-mass ratio of sand after flowing increases with the electric field intensity strengthen at different electric field strength.
keynote
Numerical simulation of Aeolian field in wind-blown sand flux based on particle tracking method1
Li Xie2, Jun Zhou, Li'an Mu
College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000, China
Key Laboratory of Mechanics on Environment and Disaster in Western China, Ministry of Education, China
1 Supported by the grant of the National Natural Science Foundations of China (No.11472122)
2 Corresponding author, email: xieli@lzu.edu.cn
The sand particles can be electrified due to the transportation back to date 1888. The charges carried by the sand particles moving in the air will form a electric field, which is call the Aeolian electric field. In 1914, Rudge observed the atmospheric field due to the presence of dust, and he found that the Aeolian electric field can reach up to 10kV/m in the severe dust storm. Actually before Rudge's observation, M. Smith already observed the same thing during dust storms happened in India, and he found that the potential would often run up so rapidly and was impossible to measure. Zheng's research group in Lanzhou University of China conducted out a series of detailed experiments in wind tunnel on the wind sand electrification. They found that the Aeolian electric field produced by the mixed-size sand particles is much stronger than the one produced by the uniform sand particles, and the relative humidity (RH) has a significant effect on the Aeolian electric field. However, there is not any numerical simulation of the Aeolian electric field to investigate it. In this paper, the effect of the RH on the Aeolian electric field was directly numerically simulated based on a particle tracking method, and we found that the Aeolian electric field rapidly rises up with the RH increasing, and reaches up to the maximum value when the RH is in region (20%, 40%), and when the RH crosses through that region, the Aeolian electric field decreases with the RH increasing, which is also observed in previous experiment. The results indicate that the trend of the Aeolian electric field dependent on the RH correlates with the charges carried by the sand particles dependent on the RH.
Electrostatic surface potential distribution of polymer film after contact charging
Yoshiaki Ota
Soka University, Japan
The charge relaxation processes was directly observed in a separation process after contact charging of polymer film. A plastic thin film was fixed on a stainless steel specimen support, then the film was made contact with a mirror polished stainless plate. In the separation process, the electrostatic potential of the specimen support was recorded with an ultra-high input impedance surface voltage meter (Trek MODEL 820). Occasionally, sometimes, sharp partial surface potential drops due to gas discharge and charge relaxation were observed. For each potential drop the amount of charge relaxation was small, which means that the gas discharge and charge relaxation takes place partially, not uniformly on the film surface, geometrically. To try to observe such trace after partial charge relaxation, we are now trying to measure the surface potential distribution of polymer film with using an electrostatic force microscope (Trek MODEL 1100TN). Some preliminary results of the ongoing project will be discussed additionally in the talk.
Numerical simulation of particle flux in a vertical pipe1
Wei Lu, Li Xie2
College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000, China
Key Laboratory of Mechanics on Environment and Disaster in Western China, Ministry of Education, China
1 Supported by the grant of the National Natural Science Foundations of China (No.11472122)
2 Corresponding author, email: xieli@lzu.edu.cn
Hopper flow is common in life, which are significantly affected by many factors, such as the charge of particle through a vertical pipe. These factors are important in granular system. In this paper, the discrete element method is used to simulate the the particle flow in a vertical pipe under a horizontal electric field considering the contact electrification produced by the collisions between the particles and the particle and the pipe wall. Simulation results show that the flux is independent on the horizontal electric field, but the charges carried by the particles after they flow out from the pipe increases with increment of the strength of the electric field. Meanwhile, simulation results found that the charge-mass ratio is also related to the particle size.
Particle-size-dependent triboelectric charging in single-component granular materials: role of humidity
Siddharth Rajupet
Case Western Reserve University, USA
Size-dependent direction of charge transfer is well documented in single-component granular systems with primarily particle-particle contacts. We investigate the effect of humidity on size-dependent charging by forming a particle fountain in a controlled humidity chamber. We drop charged particles into an electrostatic separator and examine the size distributions of the separated samples as a function of humidity. We find that for glass, at low humidity, large particles tend to charge positively while small particles tend to charge negatively, and at high humidity, we find no significant size-dependent charging.
